Flue exhaust and combustion air intake assembly for undercounter furnace

ABSTRACT

The backwall of an outer casing for a sealed-combustion furnace is provided with an opening aligned with a similar opening through the wall. A vent hood having an upper exhaust opening and a lower intake opening are adapted for mounting on the exterior of the wall. An exhaust tube connects the exhaust opening of the vent hood with the hot air flue of the furnace; and a frustum is provided at the exhaust opening on the vent hood which flares outwardly to define a base at the vent exhaust opening which has an area slightly greater than the cross-sectional area of the exhaust tube to cause the forced exhaust gases to curl about it after exiting the exhaust opening for mixing with outside gases before rising thereby reducing the temperature of the surrounding wall portion and reducing recirculation of the spent combustion gases. A curved baffle about the upper part of the intake opening also reduces recirculation under certain downward wind conditions. A thin intake conduit is formed on the inside back wall of the furnace casing which sealing communicates the annular intake space about the exhaust tube with an inlet to the fresh air blower.

[451 Feb. 22, 1972 United States Patent Honaker,.lr.

Primary Exaniiner-Charles J. Myhre Attorney-Dawson, Tilton, Fallon & Lungmus N 0 H T we B E MFM OYN CL D U MF AE TS S T U N X C E R R N MU M U.

[ STRACT The backwall of an outer casing for a sealed-combustion furnace is provided with an opening aligned with a similar opening through the wall. A vent hood having an upper exhaust opening and a lower intake opening are adapted for mounting on the exterior of the wall. An exhaust tube connects the ex- [72] Inventor: Bernard G. Honaker, Jr., Wichita, Kans.

[73] Assignee: The Coleman Company, llnc., Wichita,

Kans.

Oct. 14, 1970 [22] Filed: [211 Appl. No.:

haust opening of the vent hood with the hot air flue of the furnace; and a frustum is provided at the exhaust opening on the vent hood which flares outwardly to define a base at the vent exhaust opening which has an area slightly greater than the cross-sectional area of the exhaust tube to cause the forced exhaust gases to curl about it after exiting the exhaust opening for mixing with outside gases before rising thereby reducing the temperature of the surrounding wall portion and reducing recirculation of the spent combustion gases. A curved baffle about the upper part of the intake opening also reduces recirm & MM W B% %2 R 2 F I 6 s 10 2 13 6 6 W 332 9 e51 S n as m 5 m 8 5 w a m a 1 u C B J w T n R S m mm e D m m n R m u "h l ."f

o m cm t e U mm ll 1 2 8 6 U UH U culation under certain downward wind conditions. A thin intake conduit is formed on the inside back wall of the furnace casing which sealing communicates the annular intake space about the exhaust tube with an inlet to the fresh air blower.

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FOREIGN PATENTS OR APPLICATIONS 5 Drawing Figures 859,308 1/1961 GreatBritain........................126/85B PATENTEUFEBZZ I972 SHEET 3 OF 3 INVENTOR.

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FLUE EXHAUST AND COMBUSTION AIR INTAKE ASSEMBLY FOR UNDERCOUNTER FURNACE BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to small, compact, sealedcombustion furnaces of space heaters, such as are designed to fit beneath counters (so-called undercounter" furnaces) of recreational vehicles including travel trailers, motor homes, and campers mounted on the back of pickup trucks. The novel features of this invention also have application to other types of wall or space heaters.

2. Description of Known Systems In undercounter heaters, particularly of the type used in recreational vehicles, it is desirable to form only a single small opening through the wall of the vehicle through which fresh air is drawn and the heated flue gases are exhausted. Typically, the heated flue gases are exhausted through a central conduit and the fresh air for combustion is drawn in through an annular space about the hot exhaust tube. This insulates the wall against contact with the hot exhaust pipe, and it serves to preheat the fresh air drawn in.

The principal problems associated with the vent assembly attached to the outside of the vehicle wall are that the hot flue gases excessively heat the area surrounding the vent and that under some wind conditions the hot flue gases may be recirculated to the fresh air intake. One vent assembly for a sealed combustion wall furnace which alleviates these problems by recessing the vent is described in US. Pat. No. 3,410,193 of D. L. Clark entitled Recess Vent Assembly For Sealed Combustion Wall Furnace" and issued Nov. 12, 1968.

SUMMARY In the present invention, a single hole is formed in the wall of the recreational vehicle for both drawing in fresh air and exhausting heated flue gas, an exhaust pipe is passed through this hole for exhausting flue gases. A vent hood having an upper exhaust opening and a lower intake opening are mounted to the exterior of the vehicle wall, and a sleeve having a diameter greater than the exhaust pipe connects the exhaust pipe to the upper exhaust opening in the hood. The hood exhaust opening is formed in a segmented annulus, the center of which is fitted with a solid member of frustoconical shape with the larger base portion facing outwardly and provided with a peripheral rim. Beneath the segmented exhaust opening in the vent hood is the fresh air intake opening which communicates with an annular space about the exhaust pipe. A plate including a pocket-shaped deflector is located behind the fresh air intake opening for directing the fresh air to the annular space about the exhaust pipe.

The exhaust pipe extends through the rear wall of a sheet metal casing for the sealed combustion furnace, and on the inside of the rear wall of the casing there is a plate in which a boot-shaped recess is formed. The plate, when welded to the backwall of the casing provides an intake air duct communicating the annular space about the exhaust pipe with an opening which feeds a combustion air blower mounted within the furnace casing.

A baffle assembly in the form of a semicircular outwardly extending hood is located above the fresh air intake aperture on the vent assembly.

In operation, combustion air is drawn in by the combustion air blower through the fresh air opening in the vent hood and deflected upwardly by means of the pocket-shaped deflector into the annular space surrounding the exhaust tube. From there, the combustion air is drawn through the fresh air intake assembly located on the back of the furnace casing and into the combustion air blower. The heated flue gases are forced through the exhaust tube and thence radially outwardly by the frustoconical member adjacent the segmented annular exhaust opening. The forcing of the exhaust gases causes them to curl about the outer space of the frustum and diffuse with outside air; and this has been found to substantially reduce the temperature of the wall which is adjacent the vent hood. Further, this curling action together with the separation of exhaust gas and intake combustion air afforded by the semicircular bafile plate prevents the recirculation of flue gases into the fresh air opening in the vent hood.

Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.

THE DRAWING FIG. 1 is an upper perspective view, taken from the interior of the mobile home being heated, of a furnace incorporating the present invention;

FIG. 2 is an interior elevational view of the rear wall of the furnace casing showing the fresh air intake duct;

FIG. 3 is a side cross-sectional view of the vent hood assembly taken through the slight line 3-3 of FIG. 2;

FIG. 4 is a perspective view of portions of an undercountcr furnace incorporating the present invention with certain of the elements in exploded relation; and

FIG. 5 is a perspective view illustrating the vent hood of the present invention installed in an exterior wall of a motor home.

DETAILED DESCRIPTION A better understanding of the flue exhaust and combustion air intake assembly of the present invention will be had from a general description of the undercounter furnace for which it is designed. Only those details necessary for understanding the operation of the present invention will be described; however, further details may be obtained from a copending application of ours entitled Wall Furnace Construction With Slidable Carriage, Ser. No. 80,554, filed Oct. 14, 1970; and certain subject matter disclosed in this application is reserved for claiming in that application.

Turning then to FIG. I, an undercounter furnace is seen as including a box-shaped outer casing designated by reference numeral 10 and of generally rectilinear shape. The casing 10 includes a rear wall 11 and is provided with a front opening to which a cover panel 12 may be removably mounted by means of a conventional latch. In the upper portion of the cover panel 12 there is formed a series of louvers 13 for drawing in air from the room to be heated. Slidably received within the casing 10 is a carriage assembly generally designated by reference numeral 15 and best seen in FIG. 4. The carriage assembly of FIG. 4 includes a baseplate 16 for sliding along the bottom of the casing 10 and with upwardly turned side guide flanges l7. Mounted to the top of the baseplate I6 is a shell 18 which includes an upper hood 19, a forwardly extending horizontal separator plate 20 and two sideplates (only one of which is seen in FIG. 4 and designated 21). The shell 18, as disclosed in the above-described application, forms the interior of the casing 10 into two separate compartments when the carriage assembly is inserted therein.

Air from the room to be heated is drawn into one of the compartments over the separator plate 20 and the hood 19 into the sides of a room air blower scroll 25 and into the second compartment. Within the second compartment there is a heat exchanger and a firebox where combustion takes place. The hood 19 isenlarged to receive the heat exchanger, and combustion air is forced into a conventional burner in the firebox by means of a combustion air blower 26, also mounted upon the movable carriage assembly 18. The scroll of the combustion air blower 26 is fitted with a rearwardly extending conduit 27 communicating the side of the scroll with a rectangular air intake aperture 28. The forward outlet of the blower 26 is fed into a combustion chamber or firebox generally designated by reference numeral 30 in FIG. 1 and fitted with a suitable burner.

Referring again to FIG. 4, an exhaust extension 33 is mounted to the upper rear portion of a hood 19.

with the rear aperture 28 of the combustion air blower exten-- sion 27. Stamped in the generally L-shaped plate 35 is an inverted boot-shaped recess 40 which extends about each of the apertures 36 and 37 and forms an intake air duct when the plate 35 is welded to the backwall ll of the casing 10.

Turning now to FIG. 4, to the outside surface of the backwall ll of the casing there is secured a plate 44 in which there is formed an oval aperture 45 about which a flange 46 extends. A flange 46 is adapted to be received in a similarly shaped sleeve 47. The sleeve 47, as best seen in FIG. 3, passes through an aperture 48 in a wall W of the vehicle through which the flue gas is exhausted and fresh combustion air is drawn in. Located on the outside of the wall W is a member generally designated by reference numeral 50 in FIG. 4 having a peripheral mounting flange 51 adapted for attachment to the outer surface of wall W and defining a central aperture 52 with a rearwardly extending flange 53 adapted to be received within the sleeve 47 (see FIG. 3). Also provided in the aperture 52 of the member 50 is a pocket-shaped deflector plate 54 which extends into the aperture 48 in the wall W and is curved in transverse section.

Located in front of the pocket-shaped deflector plate 54 is an aperture 56 in a vent hood assembly generally designated 57. About the upper periphery of the fresh air intake aperture 56 there is formed an outwardly extending semicircular baffle plate 56a which is, of course, located between the fresh air intake aperture and the exhaust outlet; and its function is to assist in preventing the recirculation of heated flue gases into the combustion air intake under certain downward wind conditions. Fresh intake air, as diagrammatically illustrated by the dashed arrow 58 in FIG. 3 is drawn in by the combustion air blower deflected upwardly by the plate 54 and into the upper portion of the sleeve 47 where there is located an exhaust pipe 59 connected to the vent hood assembly by a collar 60. The fresh intake air is drawn through the annular space between the pipe 59 and the sleeve 47.

In assembled condition, the exhaust pipe 59 extends through the aperture 52 of the member 50, the aperture 45 of the plate 44 on the rear wall 11 of the casing, and telescopically receives the extension 33 mounted to the hood 19 which extends through the aperture 36 on the plate 35. The joint between the exhaust pipe 33 and the plate 35 is sealed by means of a gasket 62.

On the exterior face of the vent hood assembly 57 there is formed an exhaust aperture in the form of three segments of an annulus, the exhaust opening being generally designated by reference numeral 63. The vent hood assembly includes a cover plate 64 in which the lower intake opening 56 and the upper segmented trisection exhaust opening 63 is formed. In the illustrated embodiment the cover plate 64 is fabricated from sheet metal; however, an aluminum casing may have certain advantages.

Located in the center of the exhaust opening 63 is a solid member 65 of frustoconical shape (sometimes herein referred to as a frustum). The frustum 65 is held in place by means of the radial sections which segment the aperture 63, and is best seen in FIG. 3. The broader base section of the frustum 65 faces outwardly and is provided with a peripheral rim 68 which forms a central depression. The diameter of the frustum 65 at its base is preferably at least as great as the diameter of the exhaust pipe 59. I

Referring now to FIG. 5, there is shown an exterior view of a section of motor home in which the inventive assembly has been installed.

OPERATION In operation, fresh combustion air, as already mentioned. is drawn in through the aperture 56 in the cover plate 64 of the vent hood 57, and it is directed upwardly by the pocketshaped deflector 54 into the annular space between the ex haust pipe 59 and the sleeve 47, as schematically represented by the arrow in FIG. 3. The combustion air is then passed through the backwall l I of the casing 10 and into the fresh air intake duct 40 (see the dashed arrow 70 in FIG. 1) and thence into the rear extension 27 of the combustion air blower 26 (designated by the arrow 71 in FIG. 1). The combustion air blower 26 then delivers the fresh air into the combustion chamber 30 where combustion takes place.

The heated flue gases are routed through the heat exchanger and into the exhaust extension 33 at the top of the hood 18. The flue gases are then exhausted through the exhaust pipe 59 and the segmented annular aperture 63. The frustum 65 is positioned directly in front of and coaxially with the exhaust pipe 59; and it is oriented so that its smaller base faces and is centered relative to the exhaust pipe. The diameter of the larger, outer base of the frustum 65, as already mentioned, is equal to or slightly greater than the diameter of the exhaust pipe 59. When flow is established by the combustion blower wheel, the heated flue gases flow around the frustum, as schematically designated by the arrows 73 in FIG. 3. That is, a region of relatively low pressure is developed at the outer surface of the frustum 65 in the depression defined by the rim 68. This low-pressure region causes the flow to curl back around the frustum so that it is not dispersed appreciably toward the sides of the vent hood. Thus, the heated flue gases are mixed with the cool outsidev air prior to rising. Toward the lower portion of the exhaust outlet the gases are drawn upwardly to prevent recirculation of the spent air into the fresh air intake aperture 56.

The baffle plate 56a together with the curling effect of the exhaust gases as just described prevents recirculation of the heated flue gases into the combustion air intake conduit, particularly under certain downward wind conditions.

Having thus described in detail a preferred embodiment of the invention persons skilled in the art will be able to modify certain of the structure which has been described and to substitute elements which are of the equivalent of those disclosed; and it is, therefore, intended that all such modifications and substitutions be covered as they are embraced within the spirit and scope of the invention.

I claim:

1. In combination with a sealed combustion furnace having a combustion air blower for drawing in fresh air and forcing spent combustion gases through an exhaust conduit; a casing for said furnace; a vent hood adapted for attachment on the exterior of a wall and defining an exhaust aperture and a combustion air intake aperture beneath said exhaust aperture; an exhaust pipe for extending through said wall and said furnace casing for connecting said exhaust conduit of said furnace to said exhaust aperture on said vent hood; a frustum mounted in said exhaust aperture and having a smaller and a larger base, said larger base having an area at least about as great as the area of said exhaust pipe and being located centrally of said exhaust aperture, said exhaust aperture extending beyond said larger base of said frustum; means defining an annular intake air conduit about said exhaust pipe; intake air duct means attached to the inner wall of said furnace casing for communicating said annular intake air conduit about said exhaust tube with said intake air blower; and a baffle member extending outwardly from the upper periphery of said air intake aperture whereby combustion air is drawn by said blower through said intake aperture, deflected upwardly into said annular conduit about said exhaust pipe; then forced through said intake air duct on the rear wall of said furnace to said blower, and the heated flue gases are forced through said exhaust pipe and said exhaust outlet aperture to curl about said frustum and thereby reduce the temperature of adjacent wall areas and prevent recirculation of the flue gases into said intake aperture.

2. The combination of claim 1 wherein the exhaust outlet in said vent hood is in the form of a segmented annulus, the sections between the segmented openings supporting said haust pipe.

frustum, and wherein the larger, outer base of said frustum is provided with a peripheral rim which defines a central lowpressure recess for further-prompting the curling of heated flue gases about said base and mix the same with outside air while preventing recirculation thereof.

3. The combination of claim 1 further comprising a deflector plate behind said intake aperture of said vent hood for deflecting intake air into said annular conduit about said ex- 4. The combination of claim 3 wherein said deflector plate comprises a pocket-shaped deflector extending inwardly of said intake aperture and upwardly thereof into said annular space about said exhaust pipe said deflector plate being pocket shaped to prevent the entrance of rain into said wall opening.

5. The combination of claim I wherein said fresh air intake duct along said furnace casing comprises a plate defining a recess encompassing a first aperture through which an exhaust pipe sealing extendsfor exhausting heated flue gases, and a second aperture adapted to removably receive an extension of said combustion air blower whereby when said plate is welded to the rear surface of said casing said recess provides an intake air duct communicating said annular space about said exhaust tube with said second aperture of said plate via said recess.

6. In a sealed-combustion furnace having a casing and a removable baseplate carrying a combustion air blower for drawing in fresh combustion air and for forcing spent flue gases through an exhaust extension, the improvement comprising a vent hood for attaching to the exterior of a wall through which an opening is formed, said hood defining an upper exhaust aperture and a lower combustion air intake aperture; an exhaust pipe attached to said vent hood for extension through said wall and for sealingly coupling with said exhaust extension to communicate exhaust gases through said l 6 casing and said wall to said exhaust opening; a sleeve adapted to be received in said wall opening and surrounding said exhaust pipe for providing an annular conduit thcreabout communicating said fresh air intake opening with an enlarged opening in said casing through which said exhaust pipe extends; and a sheet metal member attached to thewall side of said casing and forming a first aperture for receiving said exhaust pipe, said sheet metal member having a portion spaced from said casing to form a conduit receiving fresh air through said enlarged opening and'further defining an aperture for coupling with an extension of said combustion air blower.

7. The furnace of claim 6 further comprising a frustoconical member mounted to said hood in said exhaust opening thereof, said exhaust opening having a circumference larger than a circumference of said exhaust pipe and said frustoconical member tapering inwardly into said exhaust pipe and havhaust pipe within said sleeve.

10. The system of claim 9 baffle member extending outwardly of said vent hood about the upper periphery of saidfresh air intake opening to prevent recirculation of heated exhaust gases under certain downward wind conditions. 

1. In combination with a sealed combustion furnace having a combustion air blower for drawing in fresh air and forcing spent combustion gases through an exhaust conduit; a casing for said furnace; a vent hood adapted for attachment on the exterior of a wall and defining an exhaust aperture and a combustion air intake aperture beneath said exhaust aperture; an exhaust pipe for extending through said wall and said furnace casing for connecting said exhaust conduit of said furnace to said exhaust aperture on said vent hood; a frustum mounted in said exhaust aperture and having a smaller and a larger base, said larger base having an area at least about as great as the area of said exhaust pipe and being located centrally of said exhaust aperture, said exhaust aperture extending beyond said larger base of said frustum; means defining an annular intake air conduit about said exhaust pipe; intake air duct means attached to the inner wall of said furnace casing for communicating said annular intake air conduit about said exhaust tube with said intake air blower; and a baffle member extending outwardly from the upper periphery of said air intake aperture whereby combustion air is drawn by said blower through said intake aperture, deflected upwardly into said annular conduit about said exhaust pipe; then forced through said intake air duct on the rear wall of said furnace to said blower, and the heated flue gases are forced through said exhaust pipe and said exhaust outlet aperture to curl about said frustum and thereby reduce the temperature of adjacent wall areas and prevent recirculation of the flue gases into said intake aperture.
 2. The combination of claim 1 wherein the exhaust outlet in said vent hood is in the form of a segmented annulus, the sections between the segmented openings supporting said frustum, and wherein the larger, outer base of said frustum is provided with a peripheral rim which defines a central low-pressure recess for further prompting the curling of heated flue gases about said base and mix the same with outside air while preventing recirculation thereof.
 3. The combination of claim 1 further comprising a deflector plate behind said intake aperture of said vent hood for deflecting intake air into said annular conduit about said exhaust pipe.
 4. The combination of claim 3 wherein said deflector plate comprises a pocket-shaped deflector extending inwardly of said intake aperture and upwardly thereof into said annular space about said exhaust pipe said deflector plate being pocket shaped to prevent the entrance of rain into said wall opening.
 5. The combination of claim 1 wherein said fresh air intake duct along said furnace casing comprises a plate defining a recess encompassing a first aperture through which an exhaust pipe sealing extends for exhausting heated flue gases, and a second aperture adapted to removably receive an extension of said combustion air blower whereby when said plate is welded to the rear surface of said casing said recess provides an intake air duct communicating said annular space about said exhaust tube with said second aperture of said plate via said recess.
 6. In a sealed-combustion furnace having a casing and a removable baseplate carrying a combustion air blower for drawing in fresh combustion air and for forcing spent flue gases through an exhaust extension, the improvement comprising a vent hood for attaching to the exterior of a wall through which an opening is formed, said hood defining an upper exhaust aperture and a lower combustion air intake aperture; an exhaust pipe attached to said vent hood for Extension through said wall and for sealingly coupling with said exhaust extension to communicate exhaust gases through said casing and said wall to said exhaust opening; a sleeve adapted to be received in said wall opening and surrounding said exhaust pipe for providing an annular conduit thereabout communicating said fresh air intake opening with an enlarged opening in said casing through which said exhaust pipe extends; and a sheet metal member attached to the wall side of said casing and forming a first aperture for receiving said exhaust pipe, said sheet metal member having a portion spaced from said casing to form a conduit receiving fresh air through said enlarged opening and further defining an aperture for coupling with an extension of said combustion air blower.
 7. The furnace of claim 6 further comprising a frustoconical member mounted to said hood in said exhaust opening thereof, said exhaust opening having a circumference larger than a circumference of said exhaust pipe and said frustoconical member tapering inwardly into said exhaust pipe and having an outer base at least about as large as the circumference of said exhaust pipe to define an annular exhaust opening spaced radially outward from an extension of said exhaust pipe.
 8. The system of claim 7 further comprising an outer peripheral rim about the larger base of said frustoconical member for causing the forced exhaust gases to curl thereabout before ascending.
 9. The apparatus of claim 6 further comprising deflector means spaced inwardly of said hood adjacent said fresh air intake opening for deflecting fresh air upwardly toward said exhaust pipe within said sleeve.
 10. The system of claim 9 baffle member extending outwardly of said vent hood about the upper periphery of said fresh air intake opening to prevent recirculation of heated exhaust gases under certain downward wind conditions. 